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Javascript; Browser Detection and Page Redirection

A recent project was ... using Internet Explorer 5.5 as ... of choice. Aware of browser ... viewing theweb page using three other commonly used ... ... 4

A recent project was developed using Internet Explorer 5.5 as the
browser of choice. Aware of browser incompatibilities, viewing the
web page using three other commonly used browsers, Internet
Explorer 4.0, Netscape Navigator 6.1, and Netscape Navigator 4.7
revealed some 'distortions'. This was mainly due to whether or not
a particular browser could interpret style sheets, and if so how the
style sheets were interpreted.

It was apparent that the page code either needed to be downgraded
to the 'lowest common denominator' or alternative versions of the
web page were needed for Netscape 6.1, Netscape 4.7, and
Internet Explorer 4.0. Therefore, a version optimized for Netscape
6.1 was created, as well as another version compatible for both
Netscape 4.7 and Internet Explorer 4.0. (This was before Internet
Explorer 6.0 and Netscape 6.2 were available.)

Review of several current web sites and textbooks on Javascript
presented different approaches to writing script to first detect a
user's browser, and then depending on the browser and version,
to redirect the user to a specific page. In this particular case, none
of the recommendations or solutions were what was needed. After
a good deal of testing and re-testing, the following script examples
were assembled.

Below are five different examples / variations of some Javascript
that is to be placed on a page that is optimized for Internet Explorer
5.5. These scripts will then automatically detect the visitor's browser
and version, and then automatically direct the particular browser in
one of three directions. They are;

If a visitor is using Internet Explorer 5.5, to remain on the current page.

If a visitor is using Netscape 6.1, to be redirected to a page that has
been optimized for Netscape 6.1.

If a visitor is using Internet Explorer 4.0 or Netscape 4.7, to be
redirected to a third page that has been written specifically for
either of these browser versions.

Explanatory discussion follows the script examples.

#1

----------------------------------------------------------------
#2

---------------------------------------------------------------
#3

---------------------------------------------------------------
#4

---------------------------------------------------------------
#5

---------------------------------------------------------------

Any of these five different scripts can be utilized. These have
been compiled after many attempts at using other suggested
scripts that either were too limited, were not applicable to
identifying version 5 and higher browsers, or just did not seem to
work as anticipated.

All these scripts are a series of conditional statements, which are
read by the visitor's browser when the web page 'ie55.htm' is
loaded.

1. The browser reads the first statement and if it is Netscape 6.1,
it is redirected to the page written specifically for Netscape 6.1.
If not,

2. The browser reads the next statement and if it is Netscape 4.7,
it is redirected to the page written for the 'number 4’ version of
either Internet Explorer or Netscape Navigator. If not,

3. The browser reads the next statement and if it is Internet Explorer
4.0, it too is redirected to the page written for the 'number 4'
version of either Internet Explorer or Netscape Navigator.
And lastly,

4. If none of the statements apply, the browser will remain on the
same page that contains the script and proceed to read the
remainder of the page.

Next are several observations made after consulting several resources
(online and in print) and conducting many 'trial and error' sessions.

Peculiarities encountered that caused difficulties include;

1. Regarding the line that identifies a browser's version number

(navigator.appVersion.indexOf(" ") != -1)
Internet Explorer; you must use "MSIE 4", not "MSIE 4.0", "4", or
"4.0". The same is true whether or not this additional ‘if’ statement,
(navigator.appName.indexOf("Internet Explorer") != -1), is included
as in #1. Use "MSIE 5" to identify Internet Explorer 5.5. **See
below for more about Internet Explorer and version numbers.
Version 5.5 does not fall under the category of version 5 or higher.

Netscape Navigator; in this statement either "5.0" or "5" will work
with Netscape 6.1 resulting in directing the browser to the page
optimized for Netscape 6.1.

if (navigator.appName.indexOf("Netscape") != -1) {
if (navigator.appVersion.indexOf("5.0") != -1)
window.location="nn61.htm";
}
But in this statement, "5.0" must be used. "5" results in Netscape 4.7
being directed to the page optimized for Netscape 6.1 instead of the
page optimized for Netscape 4.7. The reason is unknown. This
peculiarity was discovered through 'trial and error'.

if (navigator.appName.indexOf("Netscape") != -1) {
if (navigator.appVersion.indexOf("5.0") == -1)
window.location="ienn4.htm";
}
** NOTE: Attempting to separate browsers based upon their version
number is not as straight forward as it might seem. The reason is that
both Internet Explorer 4.0 and Internet Explorer 5.5 have the same
version number of 4! Also Netscape 6.1 has a version number of 5!
So trying to detect and then select browsers based on version numbers
results in confusion. In particular

The version number of '5 and higher' will exclude Internet Explorer 5.5
The version number of '4 and lower' will include Internet Explorer 5.5
The version number of '6 and higher' will exclude Netscape 6.1

2. Regarding the line that identifies a browser's name

(navigator.app.Name.indexOf(" ") != -1)

Internet Explorer; you must use "Internet Explorer", "Microsoft", or
"Microsoft Internet Explorer". "MSIE" is not recognized.

3. All of these browsers, Netscape 4.7 and 6.1, and Internet
Explorer 4.0 and 5.5, have the same code name of Mozilla.

Therefore these browsers can not differentiated based on their
code name.

Conclusions;

Remember that these scripts are to be placed on the page that has
been optimized for viewing using the Internet Explorer 5.5 browser.

If a Netscape 6.1 browser is being used, the visitor is automatically
redirected to the page that has been optimized for Netscape 6.1.

If a Netscape 4.7 browser is being used, the visitor is automatically
redirected to the page that has been optimized for either Netscape
4.7 or Internet Explorer 4.0.

If an Internet Explorer 4.0 browser is being used, the visitor is
automatically redirected to the page that has been optimized for
either Netscape 4.7 or Internet Explorer 4.0.

If none of these three 'if' conditional statements are true, the browser
will remain on the present page and will continue on with interpreting
that page, in this case the page that has been optimized for Internet
Explorer 5.5.

To use these scripts, remember to replace the fictitious pages
"nn61.htm", "ienn4.htm", and "ie55.htm" with your actual pages.
Also if using one of these scripts on a page that is created for
viewing using a browser other than IE 5.5, further adjustments will
be necessary, as well as, then re-testing the script(s).

Remember that some of the other browser types that are in use
include, i.e. AOL, Netscape Navigator 3.0 or lower, Internet
Explorer 3.0 or lower, Opera (various versions), Web TV, Lynx,
Konqueror. All of these are used in small numbers and whether one
wants to address each one of these browsers is an individual decision.

There are different web sites that contain statistics on browser usage
that can be reviewed. The best source of information on the actual
browsers that are used to view your web site are your own visitor logs.
Check those as they may or may not agree with other published web
statistics.

Obviously Intranets are a special environment and one in which the
pages must be optimized for the particular browser that is in use on
the Intranet machines. This is a much easier situation to have to contend
with.

Unfortunately until the 'browser wars' come to an end and an 'across
the board acceptance' of the W3C's guidelines for coding is the ruleFeature Articles,
browser incompatibilities will continue to influence web page construction.

Source: Free Articles from ArticlesFactory.com

ABOUT THE AUTHOR


After being a practicing dental specialist for twenty-five years, William J. Tolson became intrigued with the Internet and web page design. Self-taught and initially designing and hand coding his own personal web sites, he now devotes all his time as an independent contractor focusing on web page design, optimization and accessibility for all.



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